This invention relates to an apparatus for controlling a lift system for recovering submerged objects. More particularly, this invention extends from and below a buoyant lift system for controlling the raising and lowering of a submerged object by a diver within viewing distance of the submerged object.
Floating structures, such as barges, pontoons and other boat-like craft have been used to support powered hoists for raising and lowering objects such as instrumentation modules, machinery, small craft, ordnance, etc., that rest on the bottom of a body of water. Hoist lines attached to the objects can bring them up to the surface zone for recovery or be used to transport them to another undersea location. The recovery or relocation procedure usually calls for: 1) locating the submerged object by sonar or visual means, 2.) moving a flotation unit carrying a hoist mechanism to a position above the object, 3.) attaching a hoist line to the object by a diver, 4.) indicating by the diver that attachment has been made by visually signaling at the surface or tugging on a messenger line extending to the flotation unit or a tethered support vessel, and 5.) raising the object above the bottom by the hoist mechanism for recovery. When an object is to be relocated or work is to be done on it at a remote site, the procedure can include: 6.) moving the flotation unit to another location, 7.) avoiding hidden submerged obstacles on the way to the other location, and 8.) lowering the object until it contacts the bottom.
Care must be taken during the initial stages of this procedure to avoid rapid or uneven, accelerations that may impart a snapping displacement of the object. These accelerations can be created as the object is being extracted or pulled from the bottom since increased levels of pulling force often are needed to extract or pull the object loose from marine sediment at the bottom (as compared to the lesser amounts of force subsequently required for supporting and raising the object in the water). The increased levels of force could rupture or tear apart some relatively delicate instrumentation packages or the unwanted accelerations created by excessive force could disengage the object from the hoist line and damage it as it impacts the bottom.
Under the current salvage procedure outlined above, the hoist mechanism is not capable of being controlled in real time to provide for specifically changed forces that are tailored to avoid excessive hoisting forces and/or snapping accelerations during the extraction of the object. Furthermore, additional precise vertical displacements of the object being recovered may need to be made to avoid other submerged obstacles or to interface it with other devices. Consequently, the current procedure can create hazardous conditions for personnel and machinery associated with the recovery operation.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a control depending from a hoist mechanism on a flotation unit that permits controlled raising and lowering of an object from the bottom by a percipient diver in close proximity to the object throughout the procedure.